[mrtg] Line rates.

[Keith Woodworth]

Been using MRTG v2.8 for the last while to monitor bandwidth on a couple
of servers and one T1. Recently started to look at a partial T3 (15Mbit)
line that we have coming into a fast ether port on a Cat5500 from a 7200.

Ive had to reverse the in-out mapping to show the traffic the right way in
the graph. But I do have a question with the speed the gragh is showing vs
acutal throughput of the line as shown by a:

sho int vlan <vlan#>

on the switch.

MRTG is reporting generally a higher bit rate than acutally seeing what is
passing on that port.

I have MaxBytes set to 1875000 to reflect the 15 Mbit line speed and have
the gragh to disply in bits.

For example right now the graph just updated and is showing 2.9 kb/s of
traffic coming into the port. Yet when I look at the port on the switch
directly doing a sho int I saw just over 1404000 bits/sec input and 189600
bit/sec outgoing. 

Is this something that MRTG does? Which is the true rate? I would assume
the data I'm seeing right on the port is the correct one and not MRTG's.

The T1 I graph is correct within a few % points as the provider of it has
MRTG setup also to graph the link so I contribute that difference to their
version of MRTG (2.5.3) and they map it to 1000 bit/sec and I graph it to
the full t1 speed of 1.5 Mbits.

Just this particular 15 mbit link is not graphing out to what is showing
on the acutal port.

Anyone have an idea on what to look at here?

Thanks,
Keith


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